Endogenous flow of amino acids in the avian ileum as influenced by increasing dietary peptide concentrations

Abstract

The aim of the present study was to establish whether feeding broiler chickens with diets containing increasing dietary peptide concentrations would cause increases in ileal endogenous amino acid flow. The flow of N and most amino acids increased quadratically (P, 0·05 to 0·001) with increasing dietary concentrations of peptides. The exceptions were the flow of threonine, serine, glycine, tyrosine and cystine, which increased linearly (P,0·001) with dietary peptide levels. Another notable exception to the general trend was the flow of proline, which was significantly higher (P, 0·01) in birds fed the protein-free diet. The amino acid profile of endogenous protein, expressed as proportion of crude protein, indicated that the ratios of threonine, glutamic acid, proline, glycine, leucine, histidine, arginine and cystine were influenced (P,0·05) with increasing dietary peptide concentrations. In general, compared with the protein-free diet, the ratios of threonine and arginine in endogenous protein were lower (P,0·05) and those of glutamic acid, glycine and histidine were greater (P,0·05) in diets with high concentrations of peptides. The ratio of proline was found to decrease (P,0·05) with increasing dietary peptide concentrations. These changes in the amino acid profile of endogenous protein are probably reflective of changes in the output of one or more of the components of endogenous protein.Overall, the present results demonstrated that increasing dietary peptide concentrations increased the flow of endogenous amino acid flow at the terminal ileum of broiler chickens in a dose-dependent manner and also caused changes in the composition of endogenous protein. The observed changes in endogenous amino flow will influence the maintenance requirements for amino acids and also have implications for the calculation of true digestibility coefficient of feedstuffs. Ileal endogenous amino acid flow: Enzyme-hydrolysed casein: ChickensDuring the digestion and absorption of ingested feed, significant amounts of endogenous N enter the gastrointestinal tract at various segments. These inevitable secretions containing N predominantly originate from various digestive secretions, mucoproteins and desquamated epithelial cells lining the gut (1,2) . A proportion of these secretions escapes digestion and re-absorption and amino acids (AA) (2) from endogenously secreted proteins that reach the terminal ileum are lost to the animal. Reliable estimates of these losses of N and AA are necessary for the calculation of true digestibility values of feed ingredients and for the determination of AA requirements by the factorial method. The true ileal AA digestibility of an ingredient is a better measure than apparent digestibility because it represents the AA actually released from dietary protein and absorbed by the animal, and yields more precise estimates of the amount of AA provided in a mixed diet.In poultry, the endogenous flow of AA has traditionally been determined by the measurement of AA excretion at the excreta level in fasted bi...

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